Driving dynamics fundamentally represents a branch of technological dynamics, that is, of the vehicle mechanics, which deals with the forces acting upon a vehicle and the vehicle motions, in turn, resulting therefrom. Driving dynamics is divided in longitudinal dynamics, transverse dynamics and vertical dynamics of a vehicle.
Longitudinal dynamics concerns itself with the interaction of driving or braking forces on the wheels and with the tractional resistances dependent on the route and operating conditions. From the longitudinal dynamics, important conclusions can thus be drawn for the fuel consumption, the acceleration capacity and the design of the drive line and brake system.
Transverse dynamics examines the forces, such as crosswind or centrifugal forces, which deviate the vehicle from the driving direction. The forces can be compensated only by lateral guiding forces of the tires or wheels, the rubber-coated wheel following, compared to its central plane under a corresponding diagonal transit angle. The dynamic wheel load, the driving and braking forces, the same as the frictional nature of the road, are also influential. Depending on the position of the center of gravity, on the striking point of the wind forces, on the construction of the wheel suspension and on the tire quality, driving properties result which, together with the driver's steering reactions to the driving behavior, allow conclusions as to maintaining the driving direction when driving straight ahead and driving stability when cornering.
Vertical dynamics analyzes the vertical forces and motions produced by unevenness of the road and by interposition of tire and truck suspension produce around the transverse axle striking vibrations and pitch vibrations which are reduced by way of vibration dampers. Around the longitudinal axle, a rolling, dependent on the axle arrangement results, which can be influenced by stabilizers when cornering.
It is sought to improve the driving dynamics by using electronic control systems it is possible to influence the longitudinal dynamics, for example by an antiblock system, the transverse dynamics by a driving dynamics control with purposeful influencing of the yawing torques by a brake engagement and the vertical dynamics by a reduction of the tendency to roll of the vehicle construction and influencing of the damping properties by electronic running gear control.
Distinction is further made between an undercontrolled and an overcontrolled vehicle, the same as a vehicle distinguished by a neutral driving behavior. A diagonal transit angle of the front wheels in an undercontrolled vehicle is larger than the diagonal transit angle of the rear wheels. This means that an undercontrolled vehicle must strive to travel a larger radius of curve than that corresponding to the driven front wheels and, at the same time, pushed outwardly via the front wheels.
In an overcontrolled vehicle, the diagonal transit angles of the rear wheels are larger than those of the front wheels and, in such an operating state, the driving behavior of the vehicle is distinguished by the vehicle striving for a smaller radius of curve than that corresponding to the driven front wheels and, in extreme situations, finally breaking away with the rear.
Contrary to this, the diagonal transit angles of the front and rear wheels of a vehicle are of the same size in a neutral driving behavior and, in extreme situations, the vehicle strives and drifts evenly and uniformly over all wheels.
Taking into consideration the above stated information, the forces acting on the vehicle during its operation and the operating state curves of a vehicle resulting therefrom can be reproduced at least approximately by way of mathematical algorithms and theoretical vehicle patterns constructed thereon in a manner such that a behavior of the vehicle in different driving situations can be theoretically represented.
Testing methods known in the practice are further used in real vehicles where the effects of a load change on the maintenance of direction and on direction behavior of a vehicle are determined. During a stationary circular motion of the vehicle, the driver deals with a disturbance or occurrence that changes the tire forces in the form of a predefined load change so as to be able to observe the vehicle and evaluate reactions on the real system after sudden load changes like gas withdrawal, gas supply or braking during a stationary cornering.
During a circular motion, if a load change is initiated by gas withdrawal or braking, there results an axle load misalignment of the rear axle upon the front axle such that the dynamic tire tread forces on the front axle become stronger while the dynamic tire tread forces on the rear axle become accordingly weaker. As a result of this axle misalignment, the lateral force potential of the wheels on the front axle become stronger corresponding to the tire behavior, and the lateral force potential of the wheels on the rear axle become weaker so that the lateral force distribution changes. The input forces on the front axle additionally produce a yawing torque during an all-wheel or front-wheel drive. As a rule, a vehicle shifts when cornering and during an acceleration phase, that is, a traction operation out of the curve and into the curve during gas withdrawal, that is, a coasting operation.
The sudden and unexpected changes of the inherent steering behavior due to changes of the tire longitudinal forces caused, for example, by a load change, are not foreseeable for the normal driver and especially hard to control in extreme situations. In normal street traffic, cornerings take place with hard to control load change reactions and a change resulting therefrom of the inherent steering behavior when passing through entrances and exits of expressways which, especially for inexperienced drivers, can lead to driving situations critical to safety under certain circumstances.
In general, all drive train influences, which act upon the vehicle and result, for example, from longitudinal forces acting on the vehicle when cornering in traction or coasting operation, the same as in case of load changes of a vehicle, change the inherent behavior of a vehicle since when cornering they change the lateral force distribution compared to a rolling operation of the vehicle free of longitudinal force when cornering.
DE 197 23 358 A1 discloses a motor-operated steering system in which, on one hand, the driver's steering movement is assisted by the motor and, on the other hand, the driving stability and driving comfort of the vehicle are increased by the fact that as a result of added steering motions performed by the motor yawing motions of the vehicle are minimized. The motions of the vehicle are, at the same time, detected by different sensors and serve as measure for added steering motions performed by the motor.
This system, however, disadvantageously has long reaction periods, since only after detection of the vehicle motions, do the steering motions to be performed by the motor generate whereby driving situations critical to safety can be prevented only to a very limited extent.
Therefore, the problem on which this invention is based is to make a method available of which the driving dynamics of a vehicle can be easily controlled with brief reaction periods so that it is possible to effectively cope with driving conditions critical to safety.